Joining stair stringers

[72_square]

I'm being brave and building my own staircase for a loft conversion. Stairs will have winders at the top and bottom with a short straight flight in the middle. I've pretty much got my head around all the staircase design, except a couple of joints. questions are:

What's the best way to join the two sections of main stringer and the easment? I was thinking of a biscuit joint perhaps, but would that be ok in tension? The wallside stringer will have to self support along the top winder edge

Secondly, I'm using timber floor treads and ply risers, the treads will be quite wide around the winders and these will again need jointing. Are biscuit joints ok for bending in this direction?

 

[big-all]

may be misunderstanding this but you can only join a stair component along the grain unless theres a mechanical support taking the weight

 

[72_square]

Having a deeper think about it, I'm going to have to use something to run alongside the stringer anyway, or else I'll have a gaping hole between the floor and stringer. I'll try and explain better:

Picture a stairs with a quarter winder at the bottom and top. The straight flight in the middle runs alongside the party wall (and can fix to it). A timber trimmer runs parallel to the stairs at the upper level. A steel support beam runs next to the outside string of the upper flight (steel beam within the floor). I'm on about the string that comes from the party wall up to the timber trimmer, parallel to the steel floor beam. If I do a standard curved string, there will be a gap between the winders and steel beam. I guess I can fix timber hangers to the face of the beam, drop them down and allow the string to fix into those. thus the string becomes less of a loadbearing element.

Confusing in words, a diagram would be easy to understand. Have I lost everyone now?

 

[Scrit]

I was thinking of a biscuit joint perhaps, but would that be ok in tension? The wallside stringer will have to self support along the top winder edge

Secondly, I'm using timber floor treads and ply risers, the treads will be quite wide around the winders and these will again need jointing. Are biscuit joints ok for bending in this direction?

Biscuit joints are really designed for carcass joints in stuff like furniture. They're OK to keep a joint straight whilst the glue sets, but you really need to use an appropriate construction glue (such as UF = urea formaldehyde) and shoot, glue and cramp until dry for maximum strength. Staircases are no place to cut corners.

Are you intending to do a curved winder with a curved stringer? If so then they're laminated which can be tricky. If not the stairs I've built to date have always been mortise and tennoned into a post at the inside of the winder, even if that is a stub post as it is difficult to achieve the load bearing strength without doinf this. Older houses rounfd here tend to use a post running floor to ceiling and infill at the side of the staircase bwtween the posts with matchboards in (T & G). Perhaps a diagram would help after all.....

Scrit